Heat exchanger for cooling gases

ABSTRACT

A heat exchanger for cooling gases and having a number of fire tubes for conducting hot gases through a cooling chamber whereby all the tubes will be subjected to substantially the same conditions with regard to the temperature and flow conditions of a cooling medium in the cooling chamber.

United States Patent [191 Kiimmel et al.

HEAT EXCHANGER FOR COOLING GASES Inventors: Joachim Kiimmel,lckenerstrasse 32, Castrop-Rauxel; Josef Miinster, Columbusstrasse 34,Dusseldorf; Josef Scharfen, Windhorststrasse 8a,

Neuss; Gert Wellensiek, Holzhausen/Ammersee, all of Germany Filed: Feb.22, 1971 Appl. No.: 117,242

Foreign Application Priority Data Feb. 23, 1970 Germany 2008311 May 26,1970 Germany 2025584 US. Cl. 165/158, 23/277 R Int. Cl. F28b 9/00 Fieldof Search 165/158-162,

165/143, 142, 156; 23/288 M, 288 L, 277 R References Cited UNITED STATESPATENTS Lueffler, Jr. et a1. 23/277 R 779,741 3 100,697 3,610,3292,329,658 3,298,358 3 ,OOO, 193 2,825 ,463

Primary ExaminerCharles .l. Myhre Assistant ExaminerTheophi1 W. Streule,Jr. Attorney, Agent, or Firm-Toren and McGeady ABSTRACT A heat exchangerfor cooling gases and having a number of fire tubes for conducting hotgases through a cooling chamber whereby all the tubes will be, subjectedto substantially the same conditions with regard to the temperature andflow conditions of a cooling medium in the cooling chamber.

18 Claims, 10 Drawing Figures PATENTEDAPR 9:914

/N VEN TORS J'OACHIM KUMMEL ATTORN PAIENIEDAPR 9 IBM SHED 2 OF 8 m 0maRmw% EMHFNK. VHSRE E N MN dfl mmmw a WEETWW wm A mmldem y T B EMENTEI]APR 9 I974 N V E N TORS KQMNEL LLENSIE (gi N Y5 HEAT EXCHANGER FORCOOLING GASES The invention relates to an apparatus for the cooling offresh cracking or other gases.

Cracking gases are ordinarily produced at high temperatures and underappropriate pressure in so-called tube furnaces. Then the gases must becooled down in an extremelyshort time to a temperature at which achemical synthesis reaction or re-formation is no longer possible, thatis to say the generated chemical condition is frozen. 7

Using conventional heat exchangers, this is effected in that the freshcracking gases are conducted through a plurality of water-cooled tubes,called fire tubes. For reasons of flow-line pattern and to save space,the known fire tubes are bundled and arranged as close as possible.Moreover the known fire tubes are arranged on the inlet side in onecommon floor and enclosed by a common jacket. I I Between the diameterof the crack pipe conducting the fresh cracking gas and the externaldiameter of the bundle of fire tubes as a rule there is a considerabledifference which is compensated by a suitable funnelshaped tube piece ora conical widening of the crack pipe. With the high speed of flow of thecracking gas in modern production plant, this is the reason for heavyeddying of the cracking gas upstream of the common floor. As a result ofthe ordinarily very incomplete diffusing action of the conical widening,the flow of cracking gas breaks away in the conical widening with highspeed of flow, and return eddies occur at this point. The return eddiescause an additional flow resistance and involved therewith an increasedtime of sojourn of the cracking gas before entering the fire tubes,which often is already sufficient to render a chemical synthesisreaction or re-formation possible for the cracking gas.

However not only do the return eddies before the common floor of thefire tubes involve the danger of re-formation of the cracking gas, butat the same time a varying thermal loading of the fire tubes and theircommon floor occurs, the heaviest heating, that is the heaviest loading,occurring in the centre of the common floor and in the centre of thebundle of fire tubes. However, at this point, in the case of watercooling, the cooling action of the water in the conventional heatexchangers is particularly weak, since the water supplied in generalfrom the periphery of the jacket must overcome the flow resistance ofmany fire tubes in order to pass into the centre of the bundle and tothe centre of the common floor. There is also the fact that steambubbles rising from the common floor and the fire tubes interfere withthe water circulation in the cooling chamber and thus further reduce thecooling action of the water.

The irregular flow conditions of the water have the result that, at atemperature below or equal to 570C and a pH value higher than or equalto seven, magnetite (F e 4) forms on the water-charged surfaces of thefire tubes which are produced exclusively E0555. Furthermore, at atemperature greater than or equal to 570C and a pH value lower than orequal to seven, a ferrous oxide (FeO) layer forms on the water-chargedsurfaces between the magnetite and the iron of the fire tube wall, whichlayer is very brittle and therefore easily chips away together with themagnetite. Thus the iron of the fire tube wall again comes directly intocontact with the cooling water, and again magnetite is produced. Thiscorrosion shortens the life of the fire tubes very considerably and isfurther reinforced by an electrochemical corrosion as a result of thedifferent so-called electric valencies' of iron and magnetite and thecooling water penetrating between the iron and the magnetite.

Moreover due to the chipping magnetite and ferrous oxide in the middleon the common floor of the fire tubes there are fonned thermallyinsulating deposits which cause varying floor temperatures, that is tosay in the case of an elevated temperature in the centre of the floorinvolve a corresponding distortion of the floor which in the extremecase leads to damage which puts the heat exchanger out of action.

The irregular flow conditions of the gas and the high times of sojourninvolved therewith have the result that cracking gas consisting forexample of C H re-forms into C H (ethane) and the free carbon atoms aredeposited as a graphite-type mass on the inner wall of the fire tubes.The graphite-type mass could perse easily be removed, if in the crackinggas there were not at the same time constituents with heavy C-fraction,that is high-boiling hydrocarbons, which as a result of their highcondensation point condense in the case of a relatively long time ofsojourn and likewise are deposited on the inner wall of the fire tubes.The deposit of free carbon atoms and of the condensate of thehigh-boiling hydrocarbons on the inner wall of the fire tubes then onthe one hand diminishes the efficiency of the heat exchanger. On theother hand the deposits on the inner wall of the fire tubes, as a resultof the now reduced or deflected cooling of the surfaces and the highinherent temperature involved therewith, cake with heavy dehydration ofthe condensed hydrocarbons into an especially unpleasant increasing dirtcoating (petroleum coke), for the removal of which mostly then a kind ofwater spray with a water pressure of 300 atmospheres is necessary.

With such wearing and soiling phenomena, what is called the tour time ofconventional heat exchangers, used for the cooling of fresh crackinggas, is correspondingly short.

The invention is therefore based upon the problem of providing anapparatus for the cooling especially of fresh cracking gases whichensures a constant uniform cooling effect with any desired constructionsize, that is to say gas throughput, gas temperatures and gas pressureof any desired magnitude.

This is achieved according to the invention, using a heat exchanger witha number of-fire tubes each having substantially the same cooling effectupon the cracking gas and for this purpose the fire tubes of the heatexchanger are arranged each in a cooling medium current which is equalas regards the temperature and the flow conditions. This results in arelative limitation of the number of fire tubes, which together with thearrangement of the fire tubes characteristic for the equal coolingaction, surprisingly also leads to the existence of equal flowconditions for the cracking gas in all fire tubes.

Favourable operating conditions are present in the case of an annulararrangement of the fire tubes and supply of the cooling medium through acentral descending pipe. In the extreme case a limitation of the numberof fire tubes to one row of tire tubes is provided here. From the onerow of fire tubes then arranged in a circle it is clear that thenecessary equal operating conditions are obtained for all fire tubes.This includes both equal cooling conditions due to overall equal flowresistance opposing the flow of the cooling medium, and equal gas flowsin the fire tubes. The equal gas fiows in the fire tubes in the case ofcircular arrangement of the fire tubes, and the ordinary hot gas inletwidening conically'towards the fire tubes, is explained by the fact thatthe flow conditions in the inlet are substantially rotation-symmetricalin relation to the central axis. The inlet openings of the circularlyarranged fire tubes are charged from a gas supply aligned with the firetubes only with gas of equal flow behaviour, so that with equal tubedimensions and surface qualities in the fire tubes, equal flowconditions establish themselves.

The rotation-symmetrical flow conditions in the widening of the gassupply circuit may be assisted by a baffle which is situated in theinlet upstream of the fire tubes. The baffle is preferably made conicaland adapted in such a way to the widening, that is to say fills thewidening to such extent, that the latter with a gas pressure of 1.6 to1.8 atm.abs. produces a chamber loading which amounts at maximum to 125mg/sec/- cum and at least 90 kg/sec/cu.m.

As a result of its relatively large volume and its form adapted to theinlet, the baffle directs the gas directly into the fire tubes and thusadvantageously prevents the return eddies which occur in conventionalcracking gas supply systems, so that diffusor angles between 60 and 100easily become possible for the conical widening of the gas inlet. Thisproperty makes the baffle, irrespective of the particular arrangement ofthe fire tubes, likewise suitable for conventional gas supply conduitsand cooling devices for gas.

However the displacement body is also particularly advantageous forcooling devices with fire tubes which are retained at their inlet endsin one common upstream floor. In this case the baffle has the additionaleffect that it imparts to the upstream floor a larger heat-emitting areathan heat absorbing area and thus extra-ordinarily good cooling. Forthis purpose the baffle is preferably so formed that the heat-emittingarea of the upstream floor is at least twice as large as its heatabsorbing area. Furthermore the baffle reinforces the common floor ofthe fire tubes in such a way that it can be extremely thin. In this casea bending resistance is imparted to the upstream floor which preventsunacceptable bulging out of the floor under the action of the coolingmedium pressure and on heating. Optionally a cup-shaped thickening ofthe floor on its side facing the coolant supply pipe will contribute tothis bending resistance. Apart from increasing the bending resistance,the thickening of the floor then has the additional advantage that itimproves the distribution of the cooling medium, issuing from the supplypipe, to the individual fire tubes.

The equal cooling effect upon the fire tubes is kept constant by anunambiguous and stable circulation of the cooling medium. As coolingmedium there serves according to choice liquid lead, liquid sodium andespecially water in natural circulation. For the cooling with water innatural circulation the fire tubes, as known per se, are held at theirinlet ends and at their outlet ends in common upstream and downstreamfloors and with an intermediate floor which encloses the coolant supplypipe and is spaced from the upstream floor. The intermediate floor mayconduct the cooling medium issuing from the supply pipe against andaccording to choice over the entire upstream floor and/or in case ofneed even to a particular extent upon heavily heated surfaces of theupstream floor.

The intermediate floor may provide guide tubes which surround each firetube in the region of maximum heat-flux density. The guide tubes ensurethat the rising cooling medium flows securely along on the fire tubesand intensively cools them. Moreover, when the fire tubes are arrangedupright with their inlet ends lowermost, the guide tubes together withthe intermediate floor form dirt pockets in which scale and the likeimpurities can collect, so that these are not deposited in thermallyinsulating manner on the upstream, that is the lower, floor.

The dirt pockets are of such size that their cleaning is not necessaryduring what is called the tour time of the apparatus. As well as thedirt pockets, according to choice a regular washing off of theinterspace between the upstream floor of the fire tubes and theintermediate floor is optionally also provided, in order to preventdeposits on the upstream floor and thus deterioration of the heattransmission to the cooling water. Then a washing and water drain-offsystem is arranged between the lower floor and the intermediate fioorfor the washing.

The fire tubes may be formed over a part of their length as doublewalled tubes, the cavity between the inner and outer walls being sealedoff both against the cooling medium and against the hot gas. Thus thethermal conductivity in the tube wall of the fire tubes, withappropriate formation and arrangement of the double wall, is reduced tosuch an extent that the temperature of the internal wall lies above themaximum occurring condensation point of the gas, while the temperatureof the outer wall lies substantially below the temperature pertaining tothe maximum condensation point, and depositing of gas leading, say, topetroleum-coke separations is prevented. With the formation as doublewalled tubes there is optionally at the same time also involved areduction of the free throughflow cross-section in the fire tubes, whichthen preferably amounts to 20 to 35 percent and in the end part of thefire tubes effects as regards the gas a higher throughflow of mass, thatis to say advantageously opposes soiling of the fire tubes.

Each cooling device according to the invention, especially in the caseof only one row of fire tubes arranged in circular form, has a limitedcooling performance which is taken into consideration in modern crackinggas generators such for example as pyrolysis furnaces by a parallelconnection of several heat exchangers. This has the additional advantagethat the inflowing cracking gas is distributed to the individual heatexchangers and thus the flow conditions are already favourablyinfluenced.

Along these lines, in contrast to conventional pyrolysis furnaces or thelike cracking gas generators having several tubes which conduct away theso-called moist cracking gas, each of these tubes is provided with atleast one heat exchanger. In the case of delivery quantities of 3,000 to8,000 kg/h per tube, each tube is preferably provided with four heatexchangers connected in parallel with one another and together forming acooler section. Moreover a horizontal or especially slightly inclinedarrangement of the fire tubes is optionally foreseen. The horizontal andslightly inclined arrangement permits, for example in the case ofpyrolysis furnaces, of setting up the entire-apparatus for the coolingof the fresh cracking gas, hereinafter called cracking gas cooler,beneath the cracking furnace. Furthermore the horizontal arrangement ofthe fire tubes is much simpler in production and maintenance than avertical arrangement.

In the case of the use of water in natural circulation and thedeliberate generation of steam to boost the cooling effect and thenatural circulation, in the approximately horizontal arrangement of thefire tubes a separation of the steam-water current is prevented by thefact that the fire tubes are provided each with a double jacket throughwhich the cooling water flows. Thus its own cooling water forcedcirculation is advantageously allocated to each individual fire tube.

A further development of the apparatus according to the inventionconsists in the provision of at least two series-connected heatexchangers with a gas exit temperature of below 500C. for the first heatexchanger. In this case the construction style of the second heatexchanger is of subordinate importance, for below 500C the cracking gasno longer reforms, so that several heat exchangers connected in parallelcan be provided with one series-connected common heat exchanger, andthis may possibly also take place even in the case of an over-long timeof sojourn of the cracking gas in the series-connected heat exchanger.In this case however precipitation of the cracking gas in theseriesconnected heat exchanger is prevented in that the thermalconductivity of the fire tubes of the seriesconnected heat exchanger isreduced, at least in the exit region, by the use of a thermallyinsulating double jacket, in such a way that the temperature on theinner wall of the fire tube lies above the maximum condensation point ofthe cracking gas, even in the case of a temperature on the outer wall ofthe fire tubes lying below the minimum cracking gas condensation point.

Some examples of apparatus constructed in accordance with the inventionare illustrated in the accompanying drawings, wherein:

FIG. 1 shows the overall side view of an apparatus;

FIG. 2 shows a partial elevation, partial longitudinal section of theapparatus of FIG. 1;

.FIG. 3 is a section taken on the line III-III in FIG.

FIG. 4 is a section showing a fire tube of another apparatus;

FIG. 5 is a section taken on the line VV in FIG. 1;

FIG. 6 shows in diagrammatic representation a part of an overallproduction plant for cracking gas;

FIG. 7 shows the fire tube of a third apparatus;

FIG. 8 shows a fourth apparatus for the cooling of fresh cracking gaseshaving several parallel-connected heat exchangers and oneseries-connected common heat exchanger, in plan view;

FIG. 9 shows the apparatus according to FIG. 8 in a view in thedirection IX-IX in FIG. 8; and,

FIG. 10 shows a heat exchanger according to FIG. 8 in an individualview.

In FIGS. 1 and 5 a cooling apparatus is shown which consists of fourheat exchangers 1 connected in parallel with one another. The heatexchangers 1 are at the same time arranged three-dimensionally parallelwith one another and connected with one another through lugs 2 and bolts22 at two positions lying one above the other in each case, forassembly. In the operational condition the heat exchangers l aresuspended on suitable connectors, cables or the like devices and thelower bolts 22 are released in each case, so that the heat exchangers lwith adequate freedom of movement are mounted for swinging in the upperlugs 2 and bolts 22. Thus displacements and variations of dimension ofthe heat exchangers occurring as a result of thermal expansion are verysimply compensated.

For the connection with the connectors or cables the heat exchangers 1are provided in the upper and especially in the lower region withtie-bolts 23. The arrangement of the tie-bolts 23 in the lower regionhere has the advantage that on heating the heat exchangers expandupwards and thus bending of the transfer conduits leading to the heatexchangers l, which are subject to a substantially higher thermalstressing than the transfer conduits leading away from the heatexchangers 1, is prevented.

The four heat exchangers 1 together form a so-called cooler section.According to FIG. 6, in a pyrolysis furnace 24 generating a crackinggas, to each so-called cracking gas pipe 25 conducting away cracking gasthere is allocated a cooler section. The fresh cracking gas is here fedwithin a cooler section to the heat exchangers l at a temperature ofbetween 830 and 850C and a pressure of between 1.6 and 1.8 atm'.abs. byway of a distributor device 3 and pipes 4 from the associated crackinggas pipe 25.

The distributor device 3 consists of an inlet flange 6 which isconnected with a corresponding flange 5 of the cracking gas pipe 25, andof a dome 7 adjoining the inlet flange 6 and connecting the pipes 4 withthe inlet flange 6.

The pipes 4 open or widen into gas-distributor cones 8. The gasdistributor cones 8 terminate according to FIG. 2 in each case in acylindrical recess 9 of a container 10 and are connected with thecontainer 10 in sealed manner by means of a sealing ring 11 and abellows 12, which at the same time has the task of compensating thermalexpansions and possibly also production tolerances. The bellows 12 ishere connected with a conduit 21 which conducts away the so-calledleakage gas which penetrates past the sealing ring 11 into the bellows12.

The container 10 consists essentially of a tubular pressure jacket 13,two floors 14 and 15 and five to twelve cooling pipes, designated asfire tubes 16, which as shown in FIG. 3 are arranged in uniformdistribution with one another, parallel with the longitudinal axis ofthe container 10 and in circular form. The fire tubes 16 are welded intothe floors 14 and 15 so that the cracking gas flowing out of theassociated distributor cone 8 flows through passage holes 17 of thefloor 14, which connect the fire tubes 16 with the distributor cone 8,into the fire tubes 16 at the rear end, in the direction of flow, of thecontainer 10.

In this action a uniform flow of the cracking gas into the tire tubes 16is ensured by a baffle body 18. For this purpose the baffle body 18 isarranged in the distributor cone 8 and in the direction flow of thecracking gas before the floor l4 and has a form conducting the crackinggas to the passage holes 17, which form in the present case is that of acone with circular base area pointing with its apex into the distributorcone 8.

In the case of a distributor cone 8 of 60 to 100 angle and with adisplacement body 18 causing a chamber loading in the distributor cone 8of 90 to 125 kg. per second and cubic metre, especially favourable flowconditions are achieved.

The cracking gas flows through the fire tubes 16, and by contact withthe cooled tube wall of the fire tubes 16, within to milliseconds, losesso much heat that a temperature of 500 to 550C is reached and thechemical condition of the cracking gas is frozen, that is to sayre-formation of the cracking gas is prevented.

The cooling of the fire tubes 16 takes place according to FIG. 2 in amanner in which cooling medium, in this case water, is conducted througha central, supply pipe 19 between the floors l4 and 15, which form aclosed space with the pressure jacket 13 of the container 10. At the endfacing the floor 14 the supply pipe 19 is connected with an intermediatefloor 20 which surrounds the fire tubes 16 with guide tubes 31 with aninterval adequate for the water throughflow for their cooling.

The water flows in natural circulation upwards through the containerformed by floors 14 and 15 and the pressure jacket 13, that is to saywhen the space formed by the floors l4 and 15 and the pressure jacket 13is filled with water, the water is warmed on the common floor 14 and onthe fire tubes 16. Thus the water experiences a corresponding upwardthrust so that it flows along the vertically arranged fire tubes 16through the guide tubes 31 and continuously cools the tubes 16. Sincethe water is introduced in the boiling condition, the heating of thewater on the common floor 14 and the fire tubes 16 leads to steamformation. As a result of the steam formation the water takes up verylarge quantities of heat on the fire tubes 16 and the floor 14. Moreoverthe steam formation reinforces the flow on the fire tubes 16, incontrast to the known cooling devices.

Particularly favourable cooling conditions are present on the floor 14if with adequate base area of the distributor cone 8 the ratio of theheat emitting surface to the heat absorbing surface is greater than 2.The heat emitting surface is the surface of the floor 14 charged withcooling medium, while the heat absorbing surface is the surface of thefloor 14 charged with cracking gas.

The guide tubes 31 together with the intermediate floor 20 at the sametime act as dirt pockets in which scale and the like impurities cancollect. This prevents these impurities from settling in thermallyinsulating manner on the floor 14 to be cooled and deteriorating theheat transmission between floor 14 and cooling medium.

The cooling medium rising as a water-steam mixture is fed throughoverflow pipes 32, which are connected in the direction of flow of thecracking gas directly upstream of the floor 15 to corresponding openingsin the pressure jacket 13, to a known evaporation drum 51, while at thesame time boiling water fills up from the evaporation drum through thesupply pipe 19.

For the maintenance and cleaning of the space formed by the floors 14and 15 in the pressure jacket 13 a washing and drainage outlet 33 isfitted to the pressure jacket 13 between the floor 14 and theintermediate floor 20, which outlet consists of a pipe and a shut-offslide valve or cock (not shown).

The cooled cracking gas issuing from the heat exchanger 1 at 360 to 450Cflows into a gas collector hood 34 flanged to the pressure jacket 13 andconverging in the direction of flow of the cracking gas, which hoodcontinues in a conduit 35. The conduit 35 opens with the conduits 35 ofthe other three heat exchangers 1 into a collector device 36 which isassembled similarly to the distributor device 3 and recombines thecracking gas current previously divided by the distributor device 3, inorder to feed it to a further cooler section or to a processingapparatus.

In a further example of the heat exchangers shown in FIG. 4, between thelower floor 40 and the upper floor 41, fire tubes are welded in aspartially double tubes, namely with an inner tube 42 and an outer tube43. In this case the fire tubes are formed as double tubes especially inthe upper part and over two-thirds of their length.

At the point where the fire tubes merge into double tubes, the innertubes 42 and the outer tubes 43 are tightly connected with one another,for example by welding, with a common transition part 44. While the firetubes then are connected in the same way as according to FIGS. 1 to 3with the lower floor 40, which is upstream in the direction of flow ofthe cracking gas, the fire tubes are tightly connected at their otherends only at by outer tube 43 to the upper floor 41. The inner tubes 42of the fire tubes are conducted out through the upper floor 41 and aretightly connected with a corresponding flange or floor 45 of the gascollector hood, which is not further illustrated in this case. Since thepressure jacket 46 and forming with the floors 40 and 41 a container forthe cooling medium, is not connected with the floor 45 but terminateswith the floor 41, thus atmospheric air can penetrate into the cavitybetween the inner tube 42 and the outer tube 43. This formation of thefire tubes, with the same operation as in the heat exchangers 1according to FIGS. 1 to 3, has the advantageous consequence that byreducing the passage of heat the temperature on the inner wall of thefire tubes, especially in their upper region, always lies above themaximum condensation point of the cracking gas, although the temperatureon the outer wall of the outer tube 43 lies substantially below thetemperature pertaining to the maximum condensation point.

The heat exchanger according to FIG. 4 differs otherwise from the heatexchangers 1 according to FIGS. 1 to 3, apart from in the fire tubes,essentially only by the supply of the cooling medium, that is to say inthe formation of the supply pipe. According to FIG. 4 the de scendingpipe 47, consists of a short pipe piece which, with similar intermediatefloor 20 and guide tubes 31, is provided with an additional floor 48 atthe end remote from the floor 40. With an entry opening 49 for thecooling medium arranged adjacent to the floor 41 in the pressure jacket46 and with an exit opening 50 arranged in the direction of flow of thecracking gas immediately upstream of the entry opening 49 in thepressure jacket 46, the additional floor 48 serves to separate theheated cooling medium from the inflowing cooling medium and thus toprevent intermixing of the two media.

In FIG. 7, similarly to FIG. 4, a fire tube formed as double tube isshown. In distinction from the double tube according to FIG. 4, in thecase of this double tube the inner tube 42 is pushed into the outer tube43 and rolled thereto at its lower end to such extent that at this pointit is firmly and at the same time sealingly connected with the outertube 43.

Furthermore in this example, similarly to the case of the heatexchangers 1 according to FIGS. 1 to 3, the gas collector hood 34 istightly connected with the container 10, while the inner tube 42, withouter tube 43 firmly and sealingly welded with the upper floor 15,extends out beyond the upper floor and is displaceably mounted in afurther floor 53 which is arranged above the upper floor in the gascollector hood 34. The displaceable mounting of the inner tube 42 in thefurther floor 53 serves for the compensation of its thermal expansion,while the floor 53 in turn serves to protect a sealing composition,which fills out the interspace between the floors 53 and 15 and in doingso encloses the inner tube 42, against the inflow of the cracking gas.

According to FIGS. 8 and 9, three cracking gas pipes 60, 61 and 62 ofthe pyrolysisfurnace 24 open into three cooler sections 63, 64 and 65each of which consists of four parallel-connected heat exchangers 66slightly inclined towards the cracking gas flow, so that to eachcracking gas pipe 60, 61, 62 there is allocated a heat exchanger 66. Theheat exchangers 66 in turn all open into a gas collector 67 which feedscracking gas issuing from the heat exchangers 66 and cooled to 450C to asubsequently placed heat exchanger 68. One common cooling watercirculation 70 represented in dot-and-dash lines is provided for all theheat exchangers 66 and 68.

According to FIG. 10 the heat exchangers 66 and the heat exchanger 68,constructed analogously with the heat exchanger 1, consist each of anumber of fire tubes 75 arranged in annular form around a central supplypipe 71 and provided with a triple jacket'72, 73, 74, and of twocylindrical housing chambers 76 and 77.

Of the housing chambers 76 and 77, the housing chamber 77 is situated atthe upstream end, in the direction offlow of the cracking gas, of eachheat exchanger 66 and 68. The housing chamber 77 has two end walls, ofwhich the rear wall encloses the tubes 74 of the fire tube jacketing andthe supply pipe 71 as a common floor 78, whilethe forward end wall 79has the same function as the floor 14 of the heat exchanger 1.

The housing chamber 76 is situated at the rear end of the heatexchangers 66 and 68 and is'further divided by an'interme diate wall 80into a forward chamber 90 and a rear chamber 91. In this case the-tubes74 of the fire tube jacketing open into the forward chamber 90 and thedescending pipe 71 opens into the rear chamber 91, while the tubes 73are conducted through the rear chamber 91. Thus in the case of anadequate seal between the tubes 73, 74 and 71 and the wall of thehousing chamber 76, water can flow from the chamber 91 by way of thesupply pipe 71 to the housing chamber 77 and from the housing chamber 77through the cavity between the tubes 73 and 74 to the housing chamberThis .water flow occurs, with a suitable water supply 92 to the chamber91 and a corresponding water outlet 93 at the chamber 90, when the tubes73 are warmed by throughflowing fresh cracking gas. Then steam forms onthe hot tubes 73, which causes a strong water flow even in the case ofan inclination of the heat exchanger of only a few degrees, for example3. Thus the end wall 79, similar to the floor 14, and the fire tubes areadequately cooled as in the heat exchanger 1.

At the same time however the tubes 12, in the region of the housingchamber 76, that is to say in the region of the cooling water enteringthe heat exchanger 66 or 68, with the tubes 72 prevent condensation ofthe cracking gas on the fire tube inner wall. in that analogously withthe FIG. 7 example they correspondingly reduce the thermal conductivityof the fire tubes 7 in the region of the housing chamber 76.

Otherwise the heat exchangers 66 and 68 differ from the heat exchanger 1only in that the intermediate space between the gas distributor cone andthe bellows is partially filled with a sealing composition. A leakageconduit 84 is connected to the remaining free part of the interspacebetween the gas distributor cone and the bellows. Steam can be injectedadditionally through the leakage conduit 84, preventing escape ofcracking gas at the point of contact, additionally sealed by a packingring 85, between the gas distributor cone and the end wall 79 if thepacking ring should be damaged.

The water drainage and washing outlet, designated in this case by 86, isexpediently situated at the lowermost point of the housing chamber 77.

Likewise the tie-rods or constant suspensions necessary for the swingingand expansion-compensating mounting of the heat exchangers 66 and 68 aresecured with the aid of straps and supports to the heat exchangers 66and 68 in such a way that each heat exchanger 66 or 68 is suspended attwo points.

In assembly the heat exchangers 66 are connected with one another in theindividual cooling sections 63, 64 and 65 through lugs 94 and bolts 95which are removed after assembly.

We claim:

1. A heat exchanger for cooling cracking gases comprising a singleannular row of vertically arranged laterally spaced fire tubes forconducting hot cracking gases therethrough first means for enclosingsaid row of fire tubes and forming a cooling passageway for passing acooling medium over the exterior of said fire tubes, said first meanscomprising a vertically arranged jacket laterally enclosing said row offire tubes, an upstream floor extending transversely of and secured tosaid jacket and the lower ends of said fire tubes secured to andcommunicating through said upstream floor, a downstream floor extendingtransversely of and secured to said jacket and the upper ends of saidfire tubes secured to and communicating through said downstream floor,an intermediate floor extending transversely of said jacket between saidupstream and downstream floors and located adjacent said upstream floor,said fire tubes extending through said intermediate floor, second meansincluding a supply pipe for supplying the cooling medium for flow oversaid fibre tubes, said supplypipe being vertically arranged and disposedcentrally within said row of fire tubes, said supply tube extendingdownwardly through said downstream floor and having its outlet endextending through and terminating at the lower face of said intermediatefloor, said upstream floor intermediate fioor and said jacket forming acooling medium inlet chamber arranged to receive the cooling medium fromsaid supply pipe, third means attached to the lower end of said jacketfor introducing hot gases into said fire tubes and for assuring uniformtemperature and flow conditions in the gases as they flow through saidfire tubes in indirect heat transfer relationship with the coolingmedium, said third means includes a conically shaped baffle locatedlocated centrally on and projecting downwardly from the lower face ofsaid upstream floor, the diameter of said baffle at said upstream floorbeing smaller than the inside diameter of said row of fire tubes, fourthmeans forming an annular passage through said intermediate floor abouteach said fire tube for conducting the cooling medium from the coolingmedium inlet chamber into the space between said intermediate anddownstream floors for upward flow over said fire tubes extendingtherethrough, an overflow pipe extending through said jacket andcommunicating with the upper end of the space between said intermediateand downstream floors for removing the cooling medium after its upwardflow over said fire tubes, and said fourth means comprises a sleeve-likeguide tube located about each said fire tube and having an insidediameter slightly larger than the outside diameter of said fire tubes,said guide tube secured to and extending upwardly from the upper face ofsaid intermediate floor and said intermediate floor forming an annularopening about each said fire tube affording communication between thecooling medium inlet chamber and the annular space between each saidguide tube and said fire tube which it encloses.

2. A heat exchanger, as set forth in claim 1, wherein said third meansfor introducing hot gases into said fire tubes includes a gas supplypipe spaced axially from and below the inlet ends of said fire tubes,walls forming a closed inlet chamber extending from said gas inlet pipeto the inlet ends of said fire tubes in the lower face of said upstreamfloor, said gas inlet pipe having its axis disposed centrally of theaxes of said fire tubes, said walls forming the inlet chamber include afrustoconically shaped member connected at its smaller diameter end tosaid gas inlet pipe and having its wider diameter end connected to saidupstream floor encircling the outside diameter of said row of fire tubesat their inlet ends, and said conically shaped baffle spaced radiallyinwardly from said frusto-conically shaped member and extendingdownwardly from said upstream floor for only a portion of the axiallength of said frusto-conically shaped member.

3. A heat exchanger according to claim 2, in which the conical wideningof said frusto-conically shaped member is such that with a hot gaspressure of between 1.6 and 1.8 atm.abs., there is produced a chamberloading which amounts to between 90 and 125 kg/sec.- /cu.m.

4. A heat exchanger, as set forth in claim 2, wherein the effectiveheat-emitting area of the upper face of said upstream floor is at leasttwice as large as its effective heat-absorbing area on the lower face ofsaid upstream floor.

5. A heat exchanger according to claim 4, in which the upstream floorhas said cup-shaped thickening on its side facing a supply pipe for thecooling medium.

6. A heat exchanger according to claim 4, in which a washing anddrainage outlet is arranged between the upstream flow and theintermediate floor.

7. A heat exchanger according to claim 1, in which the fire tubes areformed at least partially at their downstream ends with double walls.

8. A heat exchanger according to claim 1, in which the fire tubes areformed with double walls over at most two-thirds of their length.

9. A heat exchanger according to claim 7, in which the annular spacebetween inner wall and the outer wall of a fire tube is filled with air.

10. A heat exchanger according to claim 7, in which the inner wall ofthe double walled tube is connected by rolling or welding with theassociated outer wall.

11. A heat exchanger according to claim 7, in which the inner wallreduces the free throughflow crosssection of the fire tubes by between20 and 35 percent.

12. Gas cooling apparatus comprising several heat exchangers constructedsubstantially as described with reference to claim 1, the several heatexchangers being connected in parallel and/or in series.

13. Apparatus according to claim 12, in which there are at least twoparallel-connected heat exchangers with a common heat exchangerconnected thereafter.

14. Apparatus according to claim 12, in which, in the final heatexchanger, the fire tubes consist of several tubes of which two tubesform a double jacket through which cooling medium flows and/0r two tubesform a thermally insulating jacket.

15; Apparatus according to claim 12, in which the heat exchangers aresuspended in a manner enabling them to swing.

16. A plant comprising a furnace for producing hot gases and a number ofpipes which lead the hot gases away from the furnace for cooling, eachof such pipes being connected to a separate heat exchanger according toclaim 1, or to a separate gas cooling apparatus according to claim l2.

17. A heat exchanger, as set forth in claim 7, wherein the outer wall ofsaid double wall fire tube is sealed to said means for enclosing saidfire tubes and said inner wall extends out of the cooling passageway,and a gas collector hood arranged to receive the end of said inner wallwhich extends outwardly from the cooling passageway.

18. A heat exchanger according to claim 17, in which the inner wall isslidingly arranged in a floor of the gas collector hood and a heat-proofseal is provided between the floor of the gas collector hood and theinner wall.

1. A heat exchanger for cooling cracking gases comprising a singleannular row of vertically arranged laterally spaced fire tubes forconducting hot cracking gases therethrough, first means for enclosingsaid row of fire tubes and forming a cooling passageway for passing acooling medium over the exterior of said fire tubes, said first meanscomprising a vertically arranged jacket laterally enclosing said row offire tubes, an upstream floor extending transversely of and secured tosaid jacket and the lower ends of said fire tubes secured to andcommunicating through said upstream floor, a downstream floor extendingtransversely of and secured to said jacket and the upper ends of saidfire tubes secured to and communicating through said downstream floor,an intermediate floor extending transversely of said jacket between saidupstream and downstream floors and located adjacent said upstream floor,said fire tubes extending through said intermediate floor, second meansincluding a supply pipe for supplying the cooling medium for flow oversaid fire tubes, said supply pipe being vertically arranged and disposedcentrally within said row of fire tubes, said supply tube extendingdownwardly through said downstream floor and having its outlet endextending through and terminating at the lower face of said intermediatefloor, said upstream floor intermediate floor and said jacket forming acooling medium inlet chamber arranged to receive the cooling medium fromsaid supply pipe, third means attached to the lower end of said jacketfor introducing hot gases into said fire tubes and for assuring uniformtemperature and flow conditions in the gases as they flow through saidfire tubes in indirect heat transfer relationship with the coolingmedium, said third means includes a conically shaped baffle locatedlocated centrally on and projecting downwardly from the lower face ofsaid upstream floor, the diameter of said baffle at said upstReam floorbeing smaller than the inside diameter of said row of fire tubes, fourthmeans forming an annular passage through said intermediate floor abouteach said fire tube for conducting the cooling medium from the coolingmedium inlet chamber into the space between said intermediate anddownstream floors for upward flow over said fire tubes extendingtherethrough, an overflow pipe extending through said jacket andcommunicating with the upper end of the space between said intermediateand downstream floors for removing the cooling medium after its upwardflow over said fire tubes, and said fourth means comprises a sleeve-likeguide tube located about each said fire tube and having an insidediameter slightly larger than the outside diameter of said fire tubes,said guide tube secured to and extending upwardly from the upper face ofsaid intermediate floor and said intermediate floor forming an annularopening about each said fire tube affording communication between thecooling medium inlet chamber and the annular space between each saidguide tube and said fire tube which it encloses.
 2. A heat exchanger, asset forth in claim 1, wherein said third means for introducing hot gasesinto said fire tubes includes a gas supply pipe spaced axially from andbelow the inlet ends of said fire tubes, walls forming a closed inletchamber extending from said gas inlet pipe to the inlet ends of saidfire tubes in the lower face of said upstream floor, said gas inlet pipehaving its axis disposed centrally of the axes of said fire tubes, saidwalls forming the inlet chamber include a frusto-conically-shaped memberconnected at its smaller diameter end to said gas inlet pipe and havingits wider diameter end connected to said upstream floor encircling theoutside diameter of said row of fire tubes at their inlet ends, and saidconically-shaped baffle spaced radially inwardly from saidfrusto-conically-shaped member and extending downwardly from saidupstream floor for only a portion of the axial length of saidfrusto-conically-shaped member.
 3. A heat exchanger according to claim2, in which the conical widening of said frusto-conically shaped memberis such that with a hot gas pressure of between 1.6 and 1.8 atm.abs.,there is produced a chamber loading which amounts to between 90 and 125kg/sec./cu.m.
 4. A heat exchanger, as set forth in claim 2, wherein theeffective heat-emitting area of the upper face of said upstream floor isat least twice as large as its effective heat-absorbing area on thelower face of said upstream floor.
 5. A heat exchanger according toclaim 4, in which the upstream floor has said cup-shaped thickening onits side facing a supply pipe for the cooling medium.
 6. A heatexchanger according to claim 4, in which a washing and drainage outletis arranged between the upstream flow and the intermediate floor.
 7. Aheat exchanger according to claim 1, in which the fire tubes are formedat least partially at their downstream ends with double walls.
 8. A heatexchanger according to claim 1, in which the fire tubes are formed withdouble walls over at most two-thirds of their length.
 9. A heatexchanger according to claim 7, in which the annular space between innerwall and the outer wall of a fire tube is filled with air.
 10. A heatexchanger according to claim 7, in which the inner wall of the doublewalled tube is connected by rolling or welding with the associated outerwall.
 11. A heat exchanger according to claim 7, in which the inner wallreduces the free throughflow cross-section of the fire tubes by between20 and 35 percent.
 12. Gas cooling apparatus comprising several heatexchangers constructed substantially as described with reference toclaim 1, the several heat exchangers being connected in parallel and/orin series.
 13. Apparatus according to claim 12, in which there are atleast two parallel-connected heat exchangers with a common heatexchanger connected thereafter.
 14. Apparatus according to claim 12, inwhich, in the final heat exchanger, the fire tubes consist of severaltubes of which two tubes form a double jacket through which coolingmedium flows and/or two tubes form a thermally insulating jacket. 15.Apparatus according to claim 12, in which the heat exchangers aresuspended in a manner enabling them to swing.
 16. A plant comprising afurnace for producing hot gases and a number of pipes which lead the hotgases away from the furnace for cooling, each of such pipes beingconnected to a separate heat exchanger according to claim 1, or to aseparate gas cooling apparatus according to claim
 12. 17. A heatexchanger, as set forth in claim 7, wherein the outer wall of saiddouble wall fire tube is sealed to said means for enclosing said firetubes and said inner wall extends out of the cooling passageway, and agas collector hood arranged to receive the end of said inner wall whichextends outwardly from the cooling passageway.
 18. A heat exchangeraccording to claim 17, in which the inner wall is slidingly arranged ina floor of the gas collector hood and a heat-proof seal is providedbetween the floor of the gas collector hood and the inner wall.